Although we do have the more popular Audacity which is a very powerful audio recorder and editor itself, but if you're looking something similar in natures + comes recommended by the GNU dudes themselves ;-), then GNUSound is also a very competitive one without a doubt as well.
*. Has the ability to load and edit audio file types such MP3, WAV, OGG Vorbis, FLAC, AAC etc. But unless you have installed Lame MP3 encoder for instance, then you won't be able to load and edit MP3 files using it.
So if you want the maximum usability out of it, then make sure you have installed appropriate audio package separately. You can get more info from here.
*. Cut/Copy/Delete/Paste using the time-line window section with ease.
*. You can even import audio track inside a lot other multimedia containers using the ffmpeg libraries installed as well.
*. Amplify, Bandpass, delay, fade, normalize, reverse playback, etc are just a few of the built in tools.
*. Play and Record audios.
*. Zoom in/out.
*. Lots of selection based features such as: left, right, nudge left/right, snap to grid, etc.
*. Playback and Record supported via Alsa, OSS, Jack or Dummy audio servers.
*. Change sample rate 8/16/32, audio channels, bitrate, recording buffer size, etc via the "Preferences" window.
*. Insert or delete individual tracks.
*. Save audio track in different formats and error recovery (say to due to the application crash, etc)... are the main features to mention.
You can install GNUSound in Ubuntu 11.04 Natty Narwhal, 11.10, 10.10 and 10.04 by using the below command in your Terminal window.
sudo apt-get install gnusoundIt did crash once I was using it but other than that it was certainly quite robust and was resource friendly too.
So if you're looking for an easy to use, fast loading multitrack audio editor and a recorder for Ubuntu (it's designed for the Gnome desktop actually) that comes recommended by the GNU foundation, then GNUSound is certainly a simple yet a powerful utility which is also completely free! (including free as in freedom too :D).